It's not a PPD/Watt issue. It's an underutilization issue. Nvidia cards are typically close to 100% utilized when folding. My 7950 is always less than 50% utilized. The folding platform just doesn't seem to fully utilize AMD Cards. However, the power used by my card is correspondingly low. I'd be surprised if it uses more than 100W of power.

The thing is, when folding with my 7950, it halves production on my CPU (about 15K when not GPU folding). So, when I only have my 7950, it doesn't make any sense to GPU fold, as I have a net decrease compared to SMP-only.

CPU (smp-only) - ~15K

CPU (smp while GPU folding) ~5K
7950 - 5K
GTX295 - 14K

as you can see, while smp folding only, I get 15K. While folding with only my 7950, I get about 10K PPD. But add in the 295, and I should start to get an average of 20-25K ppd.

Eventually, the GTX295 will go into another rig (powered by an A6 APU which won't be doing -smp), and I'll fold only smp on my main rig. That combination should hopefully net me about 28-32K PPD. I'm also planning on buying a used GTX550 to throw into my HTPC solely for the purposes of folding - purportedly good for another 12K.

Yeah well, I will advise against folding on GTX 550 Ti, I had 3 and all with problems, go get yourself something else, GTX 460, GTX 470 (around 12k PPD) or best, GTX 480/GTX 560 Ti, they do around 15-17k PPD.